Research on meso-damage and strain localization of fractured sandstone after freeze-thaw cycles

In cold regions，cyclic freezing and thawing leads to rock damage and deterioration，which in turn affects the development of local strain and its loading failure characteristics. In order to evaluate the meso-damage，strain concentration and failure modes of intact/fractured rocks under different freeze-thaw(F-T) types，discontinuous jointed sandstones were prefabricated. Then the cyclic F-T and uniaxial compression tests of saturated intact，saturated fractured and ice-filled fractured specimens were carried out. The meso-images under different F-T cycles and stress states were obtained by CT technology，and the damage evolution characteristics were analyzed. Then，combined with the digital volume correlation method to quantify the three-dimensional strain distribution，the intrinsic relationship between the mesoscopic and macroscopic damage of frozen-thawed rocks was realized. The results show that：(1) The deterioration of intact rock and fractured rock mainly occurs in the periphery of the specimen and near the prefabricated fracture with low dip angle. With the increase of F-T cycle times，the heterogeneity coefficient and fracture ratio of saturated F-T rocks gradually increase，while the ice-filled F-T rock is relatively stable. (2) The statistical frequencies of von Mises equivalent strain(ε eq ) and normal strain(ε xx ， ε yy ，ε zz ) in rocks show lognormal distribution and normal distribution respectively. However，the local strain distribution of intact rock and fractured rock are different. The former forms a 75°shear band after loading，while the latter occurs strain concentration at the low dip prefabricated fracture and rock bridge area，and the range and standard deviation of ε xx are about twice that of ε yy . (3) F-T damage directly affects the strain concentration area of intact rock，and then guides the development of secondary fractures. But for fractured rocks，it can only be used as the inducement of wing crack development，and its failure mode is determined by the arrangement of prefabricated fractures. The conclusion of this paper can provide reference for exploring the mechanism of F-T damage and the method of failure prediction. © 2022 Academia Sinica. All rights reserved.